92 



ELONGATION OF THE STEM 



effected by the formation of new cells at the apex of the stem. 

 Fig. 62 shows the general features to be noticed in the tip of 

 a stem as seen in longitudinal section. New cells are being 

 formed at the apex by division just as in the case of the root. 

 Below this formative region is the zone of elongation in which 

 the cells gradually change in character so that the cortical and 



Fig. 62. Longitudinal section of the tip of a growing stem: e, epidermis 

 extending over surface of the entire tip; a, formative region; h, upper portion 

 of the zone of elongation; c, cortex; x, cells of the central region that by 

 further growth form the vascular bundles; /, first appearance of the leaves. 



central regions are apparent and in certain elongated cells we 

 note the first indication of the vascular bundles (Fig. 62, x). 

 The leaves also originate in this region through the active divi- 

 sion of the superficial cells of the stem. The branches of the 

 stem develop somewhat later in the axils of the leaves, and more 

 deeply located cells in the cortex co-operate in their formation. 

 This relationship of the leaves and branches to the stem is shown 

 in Fig. 63, which is a diagram of an elongating stem, showing the 

 relation of the apical region of the stem (a in Fig. 62), to the 

 lower and older portion. The cells in these young leaves and 

 branches by rapid division and growth soon form the character- 

 istic tissues already noted in the leaves and stems; while a cor- 

 responding growth in the cortex and adjacent regions results in 

 the formation of vascular bundles that connect the vascular 

 bundles of the stem with those of the leaves and branches. When 



